The "cat is out of the bag" is slang for saying a secret has been revealed...

Turns out that the phrase comes from the days of sail in the Royal British Navy. To say "the cat was out of the bag" referred to the moment when a cat o' nine tails (a whip used to deal out punishment) was taken from the red bag it was kept in.

Customarily the whip was kept in the bag till the offender at hand was securely tied down and prepared for a lashing. The cat o' nine tails was kept in the bag until there was absolutely no possibility of reprieve.

So once the cat was out of the bag, somebody had it coming.

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